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FZJ-2019-00512

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Die Rolle reaktiver Kohlenwasserstoffe bei der Photooxidantienbildung in ländlichen Gebieten : ein Beitrag zur Bilanzierung der photochemischen Ozonproduktion

Kramp, F. (Corresponding author)FZJ* ; Kley, D.FZJ* ; Volz-Thomas, A.FZJ*

1995
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/21298

Report No.: Juel-3050

Abstract: During a field campaign in September 1992 hydrocarbons (VOC) and other trace gases were measured simultaneously at two sites: At Kappel, a suburb of Freiburg (Black Forest) and at the TOR station Schauinsland. The VOC measurements were conducted using in situ gaschromatography. At both sites, eighteen hydrocarbons (C$_{5}$-C$_{8}$) were measured using two identical instruments with a time resolution of 0.5 h. In addition, C$_{2}$ - C$_{6}$ hydrocarbons were measured at the TOR station with a time resolution of 3h. From our long-term measurements made at Schauinsland it was found that during weak synoptic conditions a thermal up-slope wind system usually establishes in the morning after the break-up of the nocturnal inversion. This up-slope brings polluted air from the nearby city of Freiburg through Kappel to the station. Hence, the measurements at Kappel and at Schauinsland allow to determine the decay of hydrovarbons during transport. Most hydrocarbons are oxidized in the troposphere by reaction with hydroxyl radicals (OH). 'Therefore the concentration of OH can determined from the decay of individual hydrocarbons in an air mass that travels from a location A to another location B by the slope of a semilogarithmic plot against the respective rate coefficients. Provided that the traveling time between A and B (t$_{B}$-t$_{A}$) is known and the dilution can be described as a flux out of thevolume considered, the dilution factor is then obtained from the intercept with the y-axis. The required traveling time of the air masses was determined from the wind speed at the two sites and, in addition, by variation of the time lag and minimization of the residual errors. Both, the OH-concentrations and the dilution coefficients, show a diurnal variation. The OH-concentrations varied from 5.5 $\cdot$ 10$^{6}$ to 8.5 $\cdot$ 10$^{6}$ molecule cm$^{-3}$ with a maximum around noon. The dilution coefficient decreases between 11.00 and 12.00 o'clock from 12 $\cdot$ 10$^{-5}$ to 5.5 $\cdot$ 10$^{-5}$ s$^{-1}$ and remained thereafter. Comparison of production processes and losses of hydroxyl radicals reveals that the primary sources, e.g. photolysis of ozone, formaldehyde and nitrous acid cannot compensate the off losses in the presence of an average concentration of 35 ppb NO$_{x}$ and about 130 ppbC NHMC. The likely explanation is, that most of the hydroxyl radicals must be produced by radical amplification during the oxidation of hydrocarbons, as was inferred earlier from measurements of alkylnitrates made at Schauinsland. During transport from Kappel to Schauinsland about 4 peroxy radicals are, on the average, produced for each hydrocarbon molecule oxidized. Because of the high NO$_{x}$ concentrations the formed peroxy radicals react immediately with NO to produce O$_{x}$ molecules (O$_{x}$=NO$_{2}$+O$_{3}$). On the average 2.0 $\cdot$ 10$^{8}$ molecule cm$^{-3}$ s$^{-1}$ (about 30 ppb/h) of O$_{x}$ are produced during transport from Kappel to Schauinsland. Since there is no significant increase in the O$_{x}$ concentrations, the losses must compensate the amount of production. The main sinks for O$_{x}$, e.g. the reaction of NO$_{2}$ with OH-radicals and dilution provide a loss rate of about 1.5 $\cdot$ 10$^{8}$ molecules cm$^{-3}$ s$^{-1}$. Hence, 75% of the required losses are explained by measured quantities. The local ozone budget can be closed on the basis of our measurements by including surface deposition using data from the literature.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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